1. Field of Invention
The present invention relates to a structure of a 2-D (2 dimensional) demodulator for the spread spectrum Code Division Multiple Access (CDMA) system with antenna array, and more particularly to a structure of a 2-D demodulator to extract all useful information in time and space domains.
2. Description of the Prior Art
Typically, a spread spectrum CDMA system not to use antenna array generally combines and uses only the information in a time domain by RAKE receiver. On the contrary, if antenna array is used, a 2-D demodulator of a special type to use simultaneous utilization of information in a space domain as well as in a time domain is required. Up to now, antenna array in the mobile communication systems has usually applied to the Time Division Multiple Access (TDMA) system. As the result, only structures of demodulators suitable for the TDMA system have been proposed. Lately, antenna array is used for the spread spectrum CDMA system. In such case, as it is based on the selection of MUSIC or more complicated direction finding algorithm for the demodulator in a base station, a question is raised for its realization. Such phenomenon may cause more serious problems in future mobile communication systems, which require high-speed data transmission. Also, such method has a problem that performance becomes degraded if the number of activated users per sector of a base station is more than the number of antenna array elements or correlated signals are incident. In addition, the method has a problem of convergence in the case of the blind algorithm which does not need separate reference signals, and calculates direct beamforming weighing factors without prediction for incoming directions.